Method for processing NDI in random access procedure and a method for transmitting and receiving a signal using the same

ABSTRACT

A method for a user equipment (UE) to transmit an uplink signal, and which includes receiving a first downlink control channel identified by a temporary cell identifier (Temporary C-RNTI) from a base station, the first downlink control channel including a first uplink grant signal having a new data indicator (NDI) with a first value; receiving a second downlink control channel identified by a cell identifier (C-RNTI) from the base station, the second downlink control channel including a second uplink grant signal having the NDI with a second value; and determining if the NDI with the second value has been toggled compared to the NDI previously received from the base station. Further, the UE ignores the NDI with the first value received through the first downlink control channel identified by the temporary cell identifier (Temporary C-RNTI). The method also includes transmitting the uplink signal based on the determining.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the U.S. provisional ApplicationNos. 61/077,989 and 61/087,153, filed on Jul. 3, 2008 and Aug. 7, 2008,respectively, which are hereby incorporated by reference as if fully setforth herein.

This application claims the benefit of the Korean Patent Application No.10-2009-0049516, filed on Jun. 4, 2009, which is hereby incorporated byreference as if fully set forth herein.

This application claims the benefit of the European Patent ApplicationNo. 09163938.5, filed on Jun. 26, 2009, which is hereby incorporated byreference as if fully set forth herein.

This application claims the benefit of the United Kingdom PatentApplication No. 0910933.1, filed on Jun. 24, 2009, which is herebyincorporated by reference as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for transmitting and receivinga signal by efficiently processing a new data indicator (NDI) receivedand stored in a user equipment (UE) during a random access procedure ofa mobile communication system, and a user equipment for the method.

2. Discussion of the Related Art

As an example of a mobile communication system to which the presentinvention can be applied, a third generation partnership project longterm evolution (3GPP LTE) communication system will be described inbrief.

FIG. 1 is a diagram illustrating a network structure of an E-UMTS(Evolved-Universal Mobile Telecommunications System) which is a mobilecommunication system. An E-UMTS is a system evolving from theconventional universal mobile telecommunication system (UMTS) and itsbasic standardization is currently handled by the 3GPP. Generally, TheE-UMTS may be called a long term evolution (LTE) system.

The E-UMTS network may largely be classified into a UMTS terrestrialradio access network (E-UTRAN) 101 and a core network (CN) 102. TheE-UTRAN 101 includes a user equipment (UE) 103, a base station (eNode-Bor eNB) 104, and an access gateway (AG) which is located at an end ofthe network and is connected to an external network. The AG 105 may beclassified into a part for handling user traffic and a part for handlingcontrol traffic. At this time, an AG for handling new user traffic maycommunicate with another AG for handling control traffic via a newinterface.

At least one cell exists in one eNB. An interface for transmitting usertraffic or control traffic may be located between eNBs. The core network(CN) 102 can include a node for user registration of other userequipment (UE) 103 and the access gateway 105. An interface fordiscriminating between the E-UTRAN 101 and the CN 102 may also be used.

Layers of a radio interface protocol between a UE and a network can beclassified into a first layer L1, a second layer L2 and a third layer L3based on three lower layers of an OSI (open system interconnection)standard model widely known in communication systems. A physical layerbelonging to the first layer L1 provides an information transfer serviceusing a physical channel. A radio resource control (hereinafter,abbreviated as ‘RRC’) layer located at the third layer plays a role incontrolling radio resources between the UE and the network. For this,the RRC layer enables RRC messages to be exchanged between the UE andthe network. The RRC layer may distributively be located at networknodes including the eNode B 104, the AG 105 and the like, or mayindependently be located at either the eNode B 104 or the AG 105.

FIG. 2 and FIG. 3 are diagrams illustrating a structure of a radiointerface protocol between a user equipment and UTRAN based on the 3GPPradio access network standard.

The radio interface protocol of FIG. 2 and FIG. 3 is horizontallydivided into a physical layer PHY, a data link layer and a networklayer, and is vertically divided into a user plane for transmitting datainformation and a control plane for transmitting control signaling. Indetail, FIG. 2 illustrates layers of the radio protocol control planeand FIG. 3 illustrates the layers of the radio protocol user plane. Theprotocol layers of FIG. 2 and FIG. 3 may be divided into a first layer(L1), a second layer (L2) and a third layer (L3) based on the threelower layers of an open system interconnection (OSI) standard modelwhich is well-known in the art of communication systems.

Hereinafter, each layer of the radio protocol control plane of FIG. 2and the radio protocol user plane of FIG. 3 will be described.

The physical layer PHY, which is the first layer, provides aninformation transfer service to an upper layer by using a physicalchannel. The physical layer is connected with a medium access control(MAC) layer located at a higher level through a transport channel, anddata between the MAC layer and the physical layer is transferred via thetransport channel. At this time, the transport channel is divided into adedicated transport channel and a common transport channel depending onchannel sharing. Between different physical layers, namely, betweenphysical layers of a transmitter and a receiver, data is transferred viathe physical channel using radio resources.

Several layers exist in the second layer. First of all, a medium accesscontrol (MAC) layer of the second layer serves to map various logicalchannels with various transport channels. Also, the MAC layer performsmultiplexing for mapping several logical channels with one transportchannel. The MAC layer is connected with an RLC layer corresponding toits upper layer through the logical channel. The logical channel isdivided into a control channel and a traffic channel depending on typesof transmitted information, wherein the control channel transmitsinformation of the control plane and the traffic channel transmitsinformation of the user plane.

The RLC layer of the second layer serves to perform segmentation andconcatenation of data received from its upper layer to control a size ofthe data so that the lower layer transmits the data to aradio-communication interval. Also, the RLC layer of the second layerprovides three action modes, i.e., a transparent mode (TM), anunacknowledged mode (UM), and an acknowledged mode (AM) to ensurevarious quality of services (QoS) required by each radio bearer (RB). Inparticular, the AM RLC layer performs a retransmission function throughautomatic repeat and request (ARQ) for reliable data transmission.

In order to effectively transmit data using IP packets (e.g., IPv4 orIPv6) within a radio-communication interval having a narrow bandwidth, aPDCP (packet data convergence protocol) layer of the second layer (L2)performs header compression to reduce the size of IP packet headerhaving relatively great size and unnecessary control information. Theheader compression is to increase transmission efficiency of theradio-communication period by allowing a packet header of data totransmit necessary information only. Also, in the LTE system, the PDCPlayer performs a security function. The security function includes aciphering function preventing the third party from performing datamonitoring and an integrity protection function preventing the thirdparty from performing data manipulation.

A radio resource control (hereinafter, abbreviated as ‘RRC’) layerlocated on the uppermost of the third layer is defined in the controlplane only and is associated with configuration, re-configuration andrelease of radio bearers (hereinafter, abbreviated as ‘RBs’) to be incharge of controlling the logical, transport and physical channels. Inthis case, the RB means a logical path provided by the first and secondlayers of the radio protocol for the data transfer between the userequipment and the UTRAN. Generally, establishing RB means a procedure ofdefining features of a radio protocol layer and channel required for aspecific service and establishing detailed parameters and action methodsof the radio protocol layer and the channel. The RB is divided into asignaling RB (SRB) and a data RB (DRB). The SRB is used as a path fortransmitting RRC message in a control plane (C-plane), and the DRB isused as a path for transmitting user data in a user plane (U-plane).

As downlink transport channels carrying data from the network to theuser equipments, there are provided a broadcast channel (BCH) carryingsystem information and a downlink shared channel (SCH) carrying usertraffic or control messages. The traffic or control messages of adownlink multicast or broadcast service may be transmitted via thedownlink SCH or an additional downlink multicast channel (MCH).Meanwhile, as uplink transport channels carrying data from the userequipments to the network, there are provided a random access channel(RACH) carrying an initial control message and an uplink shared channel(UL-SCH) carrying user traffic or control messages.

As downlink physical channels carrying information transferred to adownlink transport channel to a radio interval between a network and auser equipment, there are provided a physical broadcast channel (PBCH)transmitting information of the BCH, a physical multicast channel (PMCH)transmitting information of the MCH, a physical downlink shared channel(PDSCH) transmitting information of the PCH and the downlink SCH, and aphysical downlink control channel (PDCCH) (or DL L1/L2 control channel)transmitting information control information provided by the first layerand the second layer, such as downlink or uplink radio resourceassignment information (DL/UL scheduling grant). Meanwhile, as uplinkphysical channels transmitting information transferred to an uplinktransport channel to a radio interval between a network and a userequipment, there are provided a physical uplink shared channel (PUSCH)transmitting information of the uplink SCH, a physical random accesschannel (PRACH) transmitting RACH information, and a physical uplinkcontrol channel transmitting control information provided by the firstlayer and the second layer, such as HARQ ACK or NACK, scheduling request(SR), and channel quality indicator (CQI) report.

Hereinafter, a random access procedure provided by the LTE system willbe described based on the aforementioned description.

First of all, the user equipment performs a random access procedure incase of the following cases:

-   -   when the user equipment performs initial access as the user        equipment is not RRC connected with the base station;    -   when the user equipment first accesses a target cell during a        handover procedure;    -   when a random access procedure is requested by a command of the        base station;    -   when data to be transmitted to an uplink occurs in a state that        time synchronization of an uplink is not appropriate or a        designated radio resource is not assigned; and    -   when the user equipment performs a recovery procedure during a        radio link failure or handover failure.

The LTE system provides both a contention based random access procedureand a non-contention based random access procedure during a procedure ofselecting a random access preamble. In the contention based randomaccess procedure, the user equipment randomly selects one preamble froma specific set and uses the selected preamble. In the non-contentionbased random access procedure, the base station uses a random accesspreamble assigned to a specific user equipment. However, thenon-contention based random access procedure can be used only in theaforementioned handover procedure or as requested by a command of thebase station.

Meanwhile, the procedure of performing random access in the userequipment with a specific base station includes the steps of (1)transmitting a random access preamble from the user equipment to thebase station (“first message (message 1)” transmitting step), (2)receiving a random access response message from the base station inresponse to the transmitted random access preamble (“second message(message 2)” receiving step), (3) transmitting an uplink message usinginformation received in the random access response message (“thirdmessage (message 3)” transmitting step), and (4) receiving a messagecorresponding to the uplink message from the base station (“fourthmessage (message 4)” receiving step).

In a next generation mobile communication system including the LTEsystem, a hybrid automatic repeat request (HARQ) method is used as amethod for efficiently performing uplink and/or downlink signaltransmission including the aforementioned random access procedure. TheHARQ method is a combined type of an ARQ scheme and a forward errorcorrection (FEC) scheme. According to the ARQ scheme, a transmitterretransmits a signal of a receiver, which is failed in reception, byfeeding ACK/NACK signal back depending on whether a received signal issuccessfully decoded. The FEC scheme is to acquire coding gain and/orSINR gain by combining the failed signal with the retransmitted signalto correct an error of the received signal. In order to perform theaforementioned HARQ scheme, the base station can transmit a new dataindicator (NDI) through the PDCCH, wherein the NDI is to indicate theuser equipment whether the user equipment performs new data transmissionor data retransmission to the uplink. Likewise, the base station cantransmit an NDI through the PDCCH, wherein the NDI is to indicate theuser equipment whether the base station performs new data transmissionor data retransmission to the downlink.

Generally, an NDI field is a 1-bit field, and is toggled in the order of0->1->0->1-> . . . whenever new data is transmitted. In case ofretransmission, the NDI field has the same value as that of initialtransmission. Namely, the user equipment compares a previouslytransmitted value with the NDI field to identify whether dataretransmission is performed.

Meanwhile, a plurality of HARQ processes are operated independentlywithin the user equipment. Since independent data transmission isperformed for each of the HARQ processes, NDI is established for each ofthe HARQ processes. In this case, a specific HARQ process may beinvolved in general uplink/downlink data transmission and receptionincluding the aforementioned random access procedure in accordance withdata. More detailed studies of an action of NDI in determining whetherthe user equipment determines retransmission during uplink/downlink datatransmission and reception after a random access procedure will berequired, wherein the NDI is received to correspond to a specific HARQprocess during the random access procedure.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a method fortransmitting and receiving a signal and a user equipment for the same,which substantially obviate one or more problems due to limitations anddisadvantages of the related art.

An object of the present invention is to provide a method fortransmitting and receiving a signal and a user equipment for the same,in which the signal is transmitted and received in accordance with anHARQ scheme by considering an action of NDI, which is received during arandom access procedure, on uplink signal transmission and downlink datareception using a HARQ scheme of a user equipment after the randomaccess procedure, and efficiently processing NDI received during arandom access procedure and NDI received after the random accessprocedure.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, amethod for transmitting an uplink signal from a user equipment (UE) to abase station comprises receiving a first uplink (UL) grant signalthrough a message identified by a temporary cell identifier (TemporaryC-RNTI) from a base station, the first uplink grant signal including anew data indicator (NDI) toggled if the base station indicates newtransmission; receiving a second uplink grant signal through a downlinkcontrol channel identified by a cell identifier (C-RNTI) from the basestation, the second uplink grant signal including a new data indicator(NDI) with a predetermined value; and determining uplink signalretransmission of the user equipment depending on whether the NDI of thesecond uplink grant signal has been toggled, wherein the UE ignores theNDI received using the temporary cell identifier.

In another aspect of the present invention, a method for receiving adownlink signal from a base station to a user equipment (UE) comprisesreceiving a first downlink (DL) assignment signal through a messageidentified by a temporary cell identifier (Temporary C-RNTI) from a basestation, the first downlink assignment signal including a new dataindicator (NDI) toggled if the base station indicates new transmission;receiving a second downlink assignment signal through a downlink controlchannel identified by a cell identifier (C-RNTI) from the base station,the second downlink assignment signal including a new data indicator(NDI) with a predetermined value; and determining downlink signalretransmission from the base station depending on whether the NDI of thesecond downlink assignment signal has been toggled, wherein the UEignores the NDI received using the temporary cell identifier.

In other aspect of the present invention, a user equipment comprises aphysical layer module including a receiving module and a transmittingmodule, the receiving module for receiving a downlink control channeland a downlink shared channel, the downlink control channel including anew data indicator (NDI) toggled if a base station indicates newtransmission; and a MAC layer module including a plurality of HARQprocess modules, a plurality of buffers respectively corresponding tothe plurality of HARQ process modules, and a single HARQ entity, theHARQ entity controlling the plurality of HARQ process modules to allow aspecific one of the HARQ process modules to process the downlink controlchannel and the downlink shared channel received by the receiving moduleand an uplink shared channel transmitted from the transmitting module,wherein the HARQ entity or the specific HARQ process module combines NDIbit value previously stored in a specific buffer corresponding to thespecific HARQ process module with NDI value received to correspond tothe specific HARQ process module to determine whether to performretransmission depending on whether the NDI bit value has been toggled,and ignores NDI received using a temporary cell identifier stored in thespecific buffer when the HARQ entity or the specific HARQ process moduledetermines whether the NDI bit value has been toggled.

According to the aforementioned embodiments of the present invention,since NDI received during a random access procedure and NDI receivedafter the random access procedure are efficiently processed, erroroperation of the user equipment can be prevented from occurring when asignal is transmitted and received in accordance with a HARQ scheme.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a diagram illustrating a network structure of an E-UMTS(Evolved-Universal Mobile Telecommunications System) which is an exampleof a mobile communication system;

FIG. 2 and FIG. 3 are diagrams illustrating a structure of a radiointerface protocol between a user equipment and UTRAN based on the 3GPPradio access network standard;

FIG. 4 is a diagram illustrating an operation procedure of a userequipment and a base station during a non-contention based random accessprocedure;

FIG. 5 is a diagram illustrating an operation procedure of a userequipment and a base station during a contention based random accessprocedure;

FIG. 6 is a diagram illustrating an uplink HARQ action scheme;

FIG. 7 is a diagram illustrating a downlink HARQ action scheme;

FIG. 8 is a diagram illustrating a method of transmitting an uplinksignal from a user equipment using a HARQ scheme in accordance with oneembodiment of the present invention;

FIG. 9 is a diagram illustrating a method of receiving a downlink signalfrom a user equipment using a HARQ scheme in accordance with anotherembodiment of the present invention;

FIG. 10 is a diagram illustrating a method of transmitting an uplinksignal from a user equipment in accordance with one embodiment of thepresent invention;

FIG. 11 is a diagram illustrating a method of receiving a downlinksignal from a user equipment in accordance with one embodiment of thepresent invention; and

FIG. 12 is a diagram illustrating a configuration of a user equipment inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

Hereinafter, the preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings. It is to beunderstood that the detailed description, which will be disclosed alongwith the accompanying drawings, is intended to describe the exemplaryembodiments of the present invention, and is not intended to describe aunique embodiment with which the present invention can be carried out.Hereinafter, the following detailed description includes detailedmatters to provide full understanding of the present invention. However,it will be apparent to those skilled in the art that the presentinvention can be carried out without the detailed matters. For example,although the following description will be made based on a mobilecommunication system of 3GPP LTE system, the following description canbe applied to other mobile communication systems except unique featuresof the 3GPP LTE system.

In some cases, to prevent the concept of the present invention frombeing ambiguous, structures and apparatuses of the known art will beomitted, or will be shown in the form of a block diagram based on mainfunctions of each structure and apparatus. Also, wherever possible, thesame reference numbers will be used throughout the drawings and thespecification to refer to the same or like parts.

Furthermore, in the following description, it is assumed that a userequipment designates a mobile or fixed type user terminal such as amobile station (MS). It is also assumed that a base station designates arandom node of a network node, such as Node B and eNode B, whichperforms communication with a user equipment.

As described above, in order to consider an action of NDI, which isreceived during a random access procedure, on uplink signal transmissionand downlink data reception using a HARQ scheme of a user equipmentafter the random access procedure, signal transmission and receptionusing the aforementioned random access procedure and HARQ scheme will bedescribed in detail.

FIG. 4 is a diagram illustrating an operation procedure of a userequipment and a base station during a non-contention based random accessprocedure.

(1) Random Access Preamble Assignment

As described above, the non-contention based random access procedure canbe performed for two cases, i.e., (1) when a handover procedure isperformed, and (2) when requested by a command of the base station. Ofcourse, the contention based random access procedure may also beperformed for the two cases.

First of all, for non-contention based random access procedure, it isimportant that the user equipment receives a designated random accesspreamble having no possibility of contention from the base station.Examples of a method of receiving a random access preamble include amethod through a handover command and a method through a PDCCH command.A random access preamble is assigned to the user equipment through themethod of receiving a random access preamble (S401).

(2) First Message Transmission

As described above, after receiving a random access preamble designatedonly for the user equipment, the user equipment transmits the preambleto the base station (S402).

(3) Second Message Reception

After the user equipment transmits the random access preamble in stepS402, the base station tries to receive its random access responsewithin a random access response receiving window indicated throughsystem information or handover command (S403). In more detail, therandom access response can be transmitted in the form of a MAC protocoldata unit (MAC PDU), and the MAC PDU can be transferred through aphysical downlink shared channel (PDSCH). Also, it is preferable thatthe user equipment monitors a physical downlink control channel (PDCCH)to appropriately receive information transferred to the PDSCH. Namely,it is preferable that the PDCCH includes information of a user equipmentwhich should receive the PDSCH, frequency and time information of radioresources of the PDSCH, and a transport format of the PDSCH. If the userequipment successfully receives the PDCCH transmitted thereto, the userequipment can appropriately receive a random access response transmittedto the PDSCH in accordance with the information of the PDCCH. The randomaccess response can include a random access preamble identifier (ID)(for example, random access preamble identifier (RA-RNTI)), uplink grantindicating uplink radio resources, a temporary C-RNTI, and timingadvance command (TAC) values.

As described above, the random access preamble identifier is requiredfor the random access response to indicate whether the uplink grant, thetemporary C-RNTI and the TAC values are effective for what userequipment as random access response information for one or more userequipments can be included in one random access response. In this case,it is assumed that the user equipment selects a random access preambleidentifier corresponding to the random access preamble selected in stepS402.

In the non-contention based random access procedure, the user equipmentcan terminate the random access procedure after determining that therandom access procedure has been normally performed by receiving therandom access response information.

FIG. 5 is a diagram illustrating an operation procedure of a userequipment and a base station during a contention based random accessprocedure.

(1) First Message Transmission

First of all, the user equipment randomly selects one random accesspreamble from a set of random access preambles indicated through systeminformation or handover command, and selects a physical RACH (PRACH)resource that can transmit the random access preamble (S501).

(2) Second Message Reception

A method of receiving random access response information is similar tothat of the aforementioned non-contention based random access procedure.Namely, after the user equipment transmits the random access preamble instep S402, the base station tries to receive its random access responsewithin a random access response receiving window indicated throughsystem information or handover command, and receives the PDSCH throughcorresponding random access identifier information (S502). In this case,the base station can receive uplink grant, a temporary C-RNTI, andtiming advance command (TAC) values.

(3) Third Message Transmission

If the user equipment receives its effective random access response, theuser equipment respective processes information included in the randomaccess response. Namely, the user equipment applies TAC and store atemporary C-RNTI. Also, the user equipment transmits data (i.e., thirdmessage) to the base station using UL grant (S503). The third messageshould include a user equipment identifier. This is because that thebase station needs to identify user equipments which perform thecontention based random access procedure, thereby avoiding contentionlater.

Two methods have been discussed to include the user equipment identifierin the third message. In the first method, if the user equipment has aneffective cell identifier previously assigned from a corresponding cellbefore the random access procedure, the user equipment transmits itscell identifier through an uplink transport signal corresponding to theUL grant. On the other hand, if the user equipment does not have aneffective cell identifier previously assigned from a corresponding cellbefore the random access procedure, the user equipment transmits itscell identifier including its unique identifier (for example, S-TMSI orrandom ID). Generally, the unique identifier is longer than the cellidentifier. If the user equipment transmits data corresponding to the ULgrant, the user equipment starts a contention resolution timer.

(4) Fourth Message Reception

After transmitting data including its identifier through UL grantincluded in the random access response, the user equipment waits for acommand of the base station for contention resolution. Namely, the userequipment tries to receive the PDCCH to receive a specific message(504). Two methods have been discussed to receive the PDCCH. Asdescribed above, if the third message is transmitted to correspond tothe UL grant using the user equipment identifier, the user equipmenttries to receive the PDCCH using its cell identifier. If the userequipment identifier is a unique identifier of the user equipment, theuser equipment tries to receive the PDCCH using a temporary cellidentifier included in the random access response. Afterwards, in caseof the first method, if the user equipment receives the PDCCH throughits cell identifier before the contention resolution timer expires, theuser equipment determines that the random access procedure has beenperformed normally, and ends the random access procedure. In case of thesecond method, if the user equipment receives the PDCCH through thetemporary cell identifier before the contention resolution timerexpires, the user equipment identifies data transferred from the PDSCH.If the unique identifier of the user equipment is included in the data,the user equipment determines that the random access procedure has beenperformed normally, and ends the random access procedure.

Meanwhile, for adaptive retransmission of the third message in theaforementioned random access procedure, the base station can transmit ULgrant signal with NDI for indicating retransmission to the userequipment. Also, the base station can transmit downlink (DL) assignmentfor receiving the PDSCH to the PDCCH of the fourth message together witha specific NDI.

Accordingly, in a state that the NDI established for a specific HARQprocess is stored during the random access procedure, the random accessprocedure is terminated by other HARQ process. Afterwards, if generaluplink signal transmission or downlink signal reception is performed,since the base station cannot identify information of the NDIestablished for HARQ process other than the HARQ process used when therandom access procedure ends, the user equipment confuses new datatransmission with data retransmission, whereby error operation of theuser equipment may occur. In more detail, HARQ action of the MAC layerin the LTE system will be described, wherein the HARQ action is dividedinto uplink data transmission and downlink data reception.

FIG. 6 is a diagram illustrating an uplink HARQ action scheme.

In order to transmit data to the base station in accordance with theHARQ scheme, the user equipment can receive UL grant information oruplink scheduling information (UL scheduling information) from the basestation through the PDCCH (S601). Generally, the UL schedulinginformation includes user equipment identifier (for example, C-RNTI orSemi-Persistent Scheduling C-RNTI), resource block assignment,transmission parameters (modulation, coding scheme and redundancyversion), and NDI. In case of the LTE system, the user equipment haseight HARQ processes which are operated synchronously with atransmission time interval (TTI). Namely, after HARQ process 1 is usedin TTI 1, HARQ process 2 in TTI 2, . . . , HARQ process 8 in TTI 8, HARQprocess 1 is used in TTI 9 and HARQ process 2 is used in TTI 10. In thisway, specific HARQ processes can be assigned in due order in accordancewith each data receiving timing point.

Furthermore, since the HARQ processes are assigned synchronously asdescribed above, the HARQ process connected with the TTI where the PDCCHhas received for initial transmission of specific data is used for datatransmission. For example, if the user equipment receives the PDCCHincluding UL scheduling information in the Nth TTI, the user equipmenttransmits data in N+4^(th) TTI. In other words, HARQ process K assignedin the N+4^(th) TTI is used for data transmission. Namely, the userequipment monitors the PDCCH every TTI to identify the UL schedulinginformation transmitted thereto, and then transmits data to the basestation through the PUSCH in accordance with the UL schedulinginformation (S602).

If the data is received from the user equipment, the base station storesthe data in a soft buffer and then tries decoding of the data. Ifdecoding of the data is successfully performed, the base stationtransmits ACK signal to the user equipment. If decoding of the data isfailed, the base station transmits NACK signal to the user equipment. InFIG. 6, as decoding of the data is failed, the base station transmitsNACK signal to the user equipment through a physical HARQ indicatorchannel (PHICH) (S603).

If the ACK signal is received from the base station, the user equipmentsenses that data transmission to the base station has been successfullycompleted, and transmits next data. However, as illustrated in FIG. 6,if the NACK signal is received from the base station, the user equipmentsenses that data transmission to the base station has been failed, andretransmits the same data in accordance with the same format or newformat (S604).

HARQ retransmission of the user equipment can be operated in accordancewith a non-adaptive mode. Namely, initial transmission of specific datacan be performed only if the PDCCH including UL scheduling informationshould be received, but retransmission can be performed even though thePDCCH is not received. According to the HARQ retransmission of thenon-adaptive mode, data retransmission is performed using the same ULscheduling information as that of the initial transmission in the TTIwhere next HARQ process is assigned, even though the PDCCH is received.

Meanwhile, HARQ retransmission of the user equipment can be operated inaccordance with an adaptive mode. In this case, transmission parametersof retransmission are received through the PDCCH. Scheduling informationincluded in the PDCCH may be different from that of initial transmissiondepending on channel status. For example, if the channel status isbetter than that of initial transmission, the user equipment commandsdata transmission at a high bit rate. On the other hand, if the channelstatus is not better than that of initial transmission, the userequipment commands data transmission at a low bit rate.

If the user equipment receives UL scheduling information through thePDCCH, the user equipment can identify whether data to be transmittedcorresponds to initial transmission or retransmission of previous data,through NDI field included in the PDCCH. The NDI field is toggled in theorder of 0->1->0->1-> . . . whenever new data is transmitted, asdescribed above. In case of retransmission, the NDI field has the samevalue as that of initial transmission. Accordingly, the user equipmentcompares the NDI field with a previously transmitted value to identifywhether data retransmission is performed.

The user equipment counts the number of transmission times(CURRENT_TX_NB) whenever transmitting data in accordance with the HARQscheme. If the number of transmission times reaches the maximum numberof transmission times (CURRENT_TX_NB) established in the RRC layer, theuser equipment deletes the data stored in the HARQ buffer.

Meanwhile, if retransmitted data is received, the base station combinesthe retransmitted data with the data stored in the soft buffer in astate that its decoding is failed, in accordance with various manners,and then tries decoding again. If decoding is successfully performed,the base station transmits ACK signal to the user equipment. If decodingis failed, the base station transmits NACK signal to the user equipment.The base station repeats the procedure of transmitting NACK signal andreceiving the retransmitted signal until decoding of the data issuccessfully performed. In the example of FIG. 6, the base station triesdecoding by combining the data retransmitted in step S604 with thepreviously received data. If decoding of the received data issuccessfully performed, the base station transmits ACK signal to theuser equipment through the PHICH (S605). Also, the base station cantransmit UL scheduling information for next data transmission to theuser equipment through the PDCCH, and can toggle the NDI to 1 toindicate that the UL scheduling information is used for new datatransmission not adaptive retransmission (S606). Then, the userequipment can transmit new data to the base station through the PUSCHcorresponding to the received UL scheduling information (S607).

FIG. 7 is a diagram illustrating a downlink HARQ action scheme.

In order to transmit data to the user equipment in accordance with theHARQ scheme, the base station can transmit downlink schedulinginformation (DL scheduling information) to the user equipment throughthe PDCCH (S701). The DL scheduling information includes user equipmentidentifier (for example, UE ID), user equipment group ID, resource blockassignment, duration of assignment, transmission parameters (modulationmode, payload size, MIMO related information, HARQ process information,and redundancy version), and NDI. In step S701 of FIG. 7, an initial NDIis set to 0.

The DL scheduling information is retransmitted through the PDCCH, andmay be varied depending on the channel status. For example, if thechannel status is better than that of initial transmission, the basestation transmits data at a high bit rate by changing modulation orpayload size. On the other hand, if the channel status is not betterthan that of initial transmission, the base station transmits data at abit rate lower than that of initial transmission.

After identifying the DL scheduling information transmitted to the userequipment by monitoring the PDCCH every TTI, if there is information ofthe user equipment in the DL scheduling information, the user equipmentreceives data from the base station through the PDSCH at the timeassociated with the PDCCH (S702). If the data is received from the basestation, the user equipment stores the data in a soft buffer and thentries decoding of the data. The user equipment transmits HARQ feedbackinformation to the base station in accordance with the decoded result(S703). Namely, if decoding of the data is successfully performed, theuser equipment transmits ACK signal to the base station. If decoding ofthe data is failed, the user equipment transmits NACK signal to the basestation. In FIG. 7, as decoding of the data received in step S702 isfailed, the user equipment transmits NACK signal to the base station.

If the ACK signal is received from user equipment, the base stationsenses that data transmission to the user equipment has beensuccessfully and transmits next data. Meanwhile, if the NACK signal isreceived from the user equipment, the base station senses that datatransmission to the user equipment has been failed, and timelyretransmits the same data in accordance with the same format or newformat (S604). In the example of FIG. 7, since the base station receivesNACK from the user equipment, the base station transmits NDI with avalue of 0, i.e., indicating retransmission to the user equipment(S704), and data is retransmitted through the PDSCH corresponding to theDL assignment information included in the PDCCH (S705).

Meanwhile, the user equipment which has received NACK signal tries toreceive retransmitted data. The user equipment can identify whether datato be transmitted corresponds to initial transmission or retransmissionof previous data, through NDI field included in the PDCCH. In thisembodiment, as the user equipment receives the PDCCH where NDI is set to0, the user equipment can identify that the received data isretransmitted data. In this case, the user equipment combines the datareceived in step S705 with the data received and stored in step S702 inaccordance with various manners, and then tries decoding again.

If decoding is successfully performed, the user equipment transmits ACKsignal to the base station (S706). The base station which has receivedthe ACK signal transmits new data to the user equipment (S708). To thisend, the base station transmits NDI toggled to 1 and DL assignmentinformation for new data reception through the PDCCH to indicate thatthe transmitted data is new data (S707).

A problem in respect of the NDI, which may occur as the aforementionedHARQ scheme is combined with the random access procedure, will bedescribed.

The user equipment transmits and receives the third message and thefourth message using UL HARQ scheme and DL HARQ scheme, respectively,during the random access procedure.

First of all, the problem in respect of the NDI in transmitting thethird message in accordance with the UL HARQ scheme will be described asfollows.

The user equipment can transmit the third message to the base stationthrough UL scheduling or UL grant included in the second messagereceived during the random access procedure. If the base station hasreceived the third message but has failed in decoding, the base stationtransmits NACK signal to the user equipment through HARQ feedback tocommand the user equipment to retransmit the third message. If the userequipment receives the HARQ NACK only, the user equipment retransmitsthe third message using radio resource and transport format indicated bythe UL grant of the second message. However, in accordance with thechannel status or scheduling policy, the base station can separatelycommand the user equipment to use UL grant separately transmitted forretransmission instead of UL grant included in the second message duringretransmission of the third message. In this case, the UL grant forretransmission of the third message is transferred to the user equipmentthrough the PDCCH masked with the temporary cell identifier of the userequipment.

It is assumed that the user equipment has transmitted the third messageto the base station during the first random access procedure under theaforementioned system and has received UL grant for retransmissionthrough the PDCCH masked with the temporary cell identifier of the userequipment in accordance with a request of retransmission. Additionally,it is assumed that it is commanded to use HARQ process “A” for UL grantfor the third message. It is also assumed that the user equipmentperforms the second random access procedure as retransmission of thethird message is failed. Moreover, it is assumed that the second randomaccess procedure has been successfully completed as the user equipmentreceives the second message and transmits the third message using HARQprocess “B” indicated through UL grant received through the secondmessage, and the base station normally receives the third message.

At this time, the base station cannot identify the first random accessprocedure of the user equipment. Namely, during the first random accessprocedure, the HARQ process “A” of the user equipment stores NDIindicated by the UL grant of the PDCCH masked with the temporary cellidentifier of the user equipment, wherein the UL grant has been receivedfor retransmission of the third message, but the base station cannotidentify information of NDI value set for HARQ processes other than theHARQ process “B” when the random access procedure is successfullycompleted.

Accordingly, after the second (or third or more) random access procedureis successfully completed, when the base station schedules a radioresource of the HARQ process “A” of the user equipment, if the basestation schedules the radio resource with NDI which is not toggled, ascompared with the NDI received during the random access procedure, aproblem occurs in that the user equipment determines the radio resourceas a radio resource for retransmission.

Next, the problem in respect of the NDI in transmitting the fourthmessage in accordance with the DL HARQ scheme will be described asfollows.

The user equipment can receive specific DL assignment through the PDCCHmasked with the temporary cell identifier to receive the fourth messageduring the random access procedure. It is assumed that the HARQ processindicated by the received specific DL assignment is “C.” The NDIindicated by the specific DL assignment can be stored using the HARQprocess “C” of the user equipment. It is assumed that the second randomaccess procedure is required as decoding of the fourth message receivedby the specific DL assignment is failed. It is also assumed that theuser equipment receives a contention resolution message using HARQprocess “D” in accordance with DL assignment indicated by the PDCCHmasked with the temporary cell identifier during the second randomaccess procedure, whereby the random access procedure is completedsuccessfully.

Afterwards, since the base station does not know the first random accessprocedure of the user equipment like the UL HARQ, the base station doesnot know the NDI value stored in the HARQ process “C” of the userequipment. Namely, if the same NDI value as that used for the HARQprocess “C” of the first random access procedure is transmitted, aproblem occurs in that the user equipment combines the data stored inthe HARQ soft buffer due to decoding failure in the first random accessprocedure with the newly received data in error.

Accordingly, one embodiment of the present invention suggests a methodfor processing NDI by ignoring NDI received and stored during a randomaccess procedure when retransmission is determined depending on togglingof the NDI value. To this end, according to one embodiment of thepresent invention, considering that the NDI value received during therandom access procedure is the NDI received through the PDCCH maskedwith the temporary cell identifier, the NDI received using the temporarycell identifier is ignored when retransmission is determined dependingon toggling of the NDI value. Namely, when it is determined whether theNDI value has been toggled, it is suggested to consider only NDIincluded in UL grant or DL assignment received through the PDCCH maskedwith a user equipment identifier (for example, C-RNTI orSPS(Semi-Persistent Scheduling) C-RNTI) after the random accessprocedure.

FIG. 8 is a diagram illustrating a method of transmitting an uplinksignal from a user equipment using a HARQ scheme in accordance with oneembodiment of the present invention.

In the random access procedure, as described above, the user equipmentcan receive UL grant signal to transmit the third message (S801). Inthis case, UL grant can be received through the PDCCH masked with atemporary cell identifier (for example, temporary C-RNTI), and caninclude the aforementioned NDI. In the embodiment of FIG. 8, it isassumed that the NDI is set to 0.

Even after the random access procedure ends, to transmit an uplinksignal, the user equipment receives the UL grant signal from the basestation and then is assigned with a radio resource (S802). After therandom access procedure ends, the UL grant can be received through thePDCCH masked with a cell identifier (for example, C-RNTI) not atemporary cell identifier. In the embodiment of FIG. 8, the NDI is setto 0 so that the base station newly transmits uplink data to the userequipment.

If the UL grant where the NDI value is set as illustrated in step S802is received, the user equipment determines whether to transmit new dataor perform data retransmission depending on whether there is the NDIvalue previously stored for the corresponding HARQ process or whetherthe previously stored NDI value has been toggled. In this case,according to this embodiment, the user equipment ignores the NDI valuereceived using the temporary cell identifier (C-RNTI) during the randomaccess procedure and determines whether the NDI value has been toggled,whereby data retransmission is determined in accordance with thedetermined result.

As described above, the NDI value can be set for each HARQ process.Accordingly, whether the received NDI value has been toggled can bedetermined depending on an NDI value previously stored to correspond toa specific HARQ process corresponding to the time when the correspondingUL grant signal is received and an NDI value of newly received UL grant.In the embodiment of FIG. 8, the NDI of 0 is received through the ULgrant received in step S802, and the NDI received in step S801 isreceived using the temporary cell identifier. However, since the NDIreceived using the temporary cell identifier is ignored when it isdetermined whether the NDI has been toggled, the corresponding NDI isregarded as the NDI initially received, whereby the user equipmenttransmits new data to the base station through the PUSCH (S804). As aresult of determining toggling of the NDI while ignoring the NDIreceived using the temporary cell identifier, if the NDI value is thesame as that previously stored to correspond to the corresponding HARQprocess, the user equipment can perform retransmission of the previouslytransmitted data.

According to this embodiment, whether the NDI value has been toggled isdetermined regardless of status and time as far as the NDI receivedusing the temporary cell identifier is ignored. Also, a plurality ofNDIs may be received using the temporary cell identifier. According tothis embodiment, it is assumed that all NDIs received using thetemporary cell identifier are ignored when it is determined whether theNDI value has been toggled. In the same manner as that of FIG. 8, amethod for receiving a downlink signal in a user equipment in accordancewith a DL HARQ scheme will be described.

FIG. 9 is a diagram illustrating a method of receiving a downlink signalfrom a user equipment using a HARQ scheme in accordance with anotherembodiment of the present invention.

The basic principle of the method illustrated in FIG. 9 is the identicalwith that of uplink signal transmission illustrated in FIG. 4. Namely,as described above, the user equipment can receive DL assignmentincluding the NDI field to receive the second message or the fourthmessage during the random access procedure (S901). In this case, DLassignment can be received through the PDCCH masked with the temporarycell identifier.

Even after the random access procedure ends, in order that the userequipment receives downlink data, the base station notifies the userequipment through what radio resource the user equipment should receivethe PDSCH, through DL assignment information, and the user equipmentreceives DL assignment information (S902). This DL assignmentinformation is received through the PDCCH masked with a cell identifier.The user equipment can receive downlink data from the base station inaccordance with the DL assignment information (S903). In this case, thePDSCH corresponding to the PDCCH received in accordance with step S902may be received before or after step S904 where it is determined whetherthe NDI value of the user equipment has been toggled.

Meanwhile, the user equipment can identify whether the received downlinkdata is newly transmitted data or retransmitted data of previous data,through the NDI field of the received DL assignment. Namely, if the NDIfield value received through DL assignment is different from thatpreviously stored to correspond to the corresponding HARQ process, theuser equipment regards the received data as new data. If the receivedNDI field value is the same as the NDI value previously stored tocorrespond to the corresponding HARQ process, the user equipment triesdecoding by combining the received data with the data stored in the softbuffer of the corresponding HARQ process. As described above, thisembodiment suggests that the user equipment ignores the NDI receivedduring the random access procedure, i.e., the NDI received using thetemporary cell identifier when determining whether the NDI valuereceived through DL assignment has been toggled. In the example of FIG.9, since the NDI field value received in step S902 is 0 and the NDIreceived in step S901 is not considered, the user equipment regards theNDI field value received in step S901 as the initially received NDI anddecodes the data received in step S903 as new data.

If the NDI received in step S901 is ignored and the NDI value receivedin step S903 is the same as the NDI value set for the corresponding HARQprocess, the user equipment can perform decoding by combining the datareceived in step S903 with the previously received data.

According to this embodiment, whether the NDI value has been toggled isdetermined regardless of status and time as far as the NDI receivedusing the temporary cell identifier is ignored. Also, if a plurality ofNDIs are received using the temporary cell identifier, this embodimentsuggests that all NDIs received using the temporary cell identifier areignored.

Meanwhile, in the aforementioned embodiments of the present invention,how to solve the aforementioned problem where the user equipmentdetermines, in error, whether the data transmitted from or received inthe user equipment is retransmitted data, due to the NDI received duringthe random access procedure, will be described in detail.

FIG. 10 is a diagram illustrating a method of transmitting an uplinksignal from a user equipment in accordance with one embodiment of thepresent invention.

The user equipment can transmit a specific random access preamble to thebase station during the random access procedure (step 1). The basestation receives the random access preamble and transmits a response tothe random access preamble to the user equipment (step 2). The responseto the random access preamble can include UL grant to allow the userequipment to transmit the third message, and in this embodiment, it isassumed that the UL grant indicates HARQ process “A.” Also, the responseto the random access preamble includes a temporary cell identifier to betemporarily used by the user equipment.

The user equipment can transmit the third message to the base stationusing the HARQ process “A” in accordance with the received UL grant(step 3). In this way, if the third message is transmitted from the userequipment, the contention resolution timer (CR timer) starts. Inspecific case, the base station receives the third message but fails todecode the third message, whereby the base station can request the userequipment to retransmit the third message.

When requesting the user equipment to retransmit the third message, thebase station can transmit UL grant for retransmission of the thirdmessage to the user equipment through the PDCCH masked with thetemporary cell identifier of the user equipment, thereby requesting aradio resource or transport format used for transmission of the thirdmessage (step 4). Also, the NDI value can be included in the UL grantfor retransmission of the third message. In this embodiment, it isassumed that the NDI value in step 4 is set to 0.

The user equipment can retransmit the third message to the base stationusing the received UL grant for retransmission of the third message(step 5).

If the started or restarted CR timer ends during transmission orretransmission of the third message, the user equipment determines thatthe random access procedure has been failed, transmits the random accesspreamble to the base station again, and receives the response to therandom access preamble from the base station (step 6).

The UL grant for transmission of the third message is included in therandom access response received in step 6. It is assumed that the ULgrant indicates HARQ process “B.” Also, the response to the randomaccess preamble includes a temporary cell identifier to be temporarilyused by the user equipment.

The user equipment transmits the third message to the base station usingthe UL grant, and the base station receives the third message,successfully performs decoding, and transmits the contention resolutionmessage to the user equipment. Then, the user equipment which hasreceived the contention resolution message determines that the randomaccess procedure has been successfully completed (step 7).

After the aforementioned random access procedure is completed, the basestation can transmit UL grant to the user equipment through the PDCCHmasked with user equipment identifier (for example, C-RNTI or SPSC-RNTI), thereby scheduling transmission of specific data (step 8). Inthis embodiment, it is assumed that the UL grant transmitted in step 8is HARQ process “A.” It is also assumed that the NDI value forindicating new data transmission is set to “0” as the base stationcannot identify information of the HARQ process “A” not used for endingthe random access procedure but used during the random access procedure.

The user equipment receives UL grant where the NDI value correspondingto the HARQ process “A” is set to “0” during the first random accessprocedure and the NDI value is again set to “0” to correspond to theHARQ process “A” after the second random access procedure. In thisembodiment, if the NDI received using the temporary cell identifier isnot ignored when it is determined whether the NDI value has beentoggled, since it is regarded that the user equipment receives UL grantwhere the NDI value has been toggled, the user equipment determines theUL grant as that for retransmission. Accordingly, the user equipmentcannot transmit new MAC PDU in accordance with the UL grant received instep 8.

However, if the user equipment receives UL grant in step 8 in accordancewith this embodiment, the user equipment ignores the NDI value for ULgrant through the PDCCH masked with a temporary cell identifier. As aresult, the user equipment determines the UL grant received in step 8 asUL grant for new transmission not retransmission. Then, the userequipment transmits new MAC PDU to the base station using the UL grantreceived in step 8 (step 9).

FIG. 11 is a diagram illustrating a method of receiving a downlinksignal from a user equipment in accordance with one embodiment of thepresent invention.

The user equipment transmits a random access preamble to the basestation during the random access procedure (step 1), and receives aresponse to the random access preamble (step 2).

The user equipment transmits the third message to the base station inaccordance with the UL grant received in the response to the randomaccess preamble, and assumes that the CR timer starts (step 3).

The user equipment can receive DL assignment of the PDDCH masked with atemporary cell identifier of the user equipment from the base station(step 4). In this embodiment, it is assumed that the DL assignmentindicates HARQ process “C.” It is also assumed that the NDI value of theDL assignment is set to “0.” Moreover, it is assumed that the userequipment receives the contention resolution message through the DLassignment but fails to decode the contention resolution message, anddetermines that the random access procedure is failed as the CR timerends. As a result, it is assumed that the user equipment tries thesecond random access procedure.

After transmitting the third message during the second random accessprocedure, the user equipment receives DL assignment of the PDCCH maskedwith a temporary cell identifier of the user equipment from the basestation, and receives the contention resolution message which includesuser equipment identifier (step 5). In this embodiment, it is assumedthat the DL assignment indicates HARQ process “D.” In this case, theuser equipment determines that the random access procedure has beensuccessfully completed.

The user equipment can receive DL assignment of the PDCCH masked withC-RNTI of the user equipment from the base station after the randomaccess procedure is performed (step 6). In this embodiment, it isassumed that the DL assignment indicates HARQ process “C,” and the NDIvalue of the DL assignment is set to “0.”

Since the data failed in decoding during the fourth message reception ofthe first random access procedure remain in the soft buffercorresponding to the HARQ process “C,” if DL assignment of the PDCCHmasked with the C_RNTI of the user equipment indicates HARQ process “C”after the random access procedure and the NDI value is set to “0” whichis not toggled, and if the NDI value received using the temporary C-RNTIis not ignored in the same manner as this embodiment, the user equipmenttries combination of the data stored in the soft buffer of the HARQprocess “C” with newly received data. However, the user equipmentaccording to this embodiment receives DL assignment after the randomaccess procedure, and ignores the NDI indicated by assignment of thePDDCH masked with a temporary C-RNTI during the random access procedurewhen determining whether the NDI value of the DL assignment has beentoggled (step 7). As a result, the user equipment determines theassignment of the PDCCH masked with the C-RNTI as DL assignment for newtransmission not retransmission, does not combine the data received instep 8 with the data stored in the HARQ soft buffer, deletes previousdata, stores the data newly received in step 8 in the soft buffer, andtries decoding.

Hereinafter, a configuration of the user equipment for uplink signaltransmission and downlink signal reception will be described.

FIG. 12 is a diagram illustrating a configuration of a user equipment inaccordance with one embodiment of the present invention.

The user equipment according to one embodiment of the present inventionincludes a physical layer module 1210 for transmitting an uplink signaland receiving a downlink signal, and a MAC layer module 1220 forperforming signal mapping between an upper layer module and the physicallayer module 1210. In more detail, the physical layer module includes areceiving module 1211 for receiving a PDCCH including an NDI toggledwhen the base station indicates new transmission and receiving a PDSCHcorresponding to the PDCCH, and a transmitting module 1212 performingPUSCH transmission corresponding UL grant received through the PDCCH.Also, the MAC layer module includes a plurality of HARQ process modules1221 and a plurality of buffers 1222 respectively corresponding to theplurality of HARQ process modules. It is assumed that the plurality ofbuffers 1222 include HARQ buffers for storing HARQ control informationassociated with the corresponding HARQ process 1221. It is also assumedthat the plurality of buffers 1222 include a soft buffer for temporarilystoring data processed by the other corresponding HARQ process 1221.

The MAC layer module 1220 further includes a single HARQ entity 1223controlling MAC layer HARQ operation of the user equipment. The HARQentity 1223 serves to control corresponding data transmission orreception to be performed through a specific one of the HARQ processes1221 considering a receiving time of the downlink signal received by thereceiving module 1221 of the physical layer module 1210.

Meanwhile, the user equipment according to this embodiment determineswhether to perform retransmission depending on whether the NDI value hasbeen toggled, by comparing the NDI value previously stored in a specificbuffer corresponding to a specific process with the NDI value receivedto correspond to the specific HARQ process. In this case, it isconfigured that the NDI received using a temporary cell identifierstored in the specific buffer is ignored when it is determined whetherthe NDI value has been toggled. Preferably, this configuration isconfigured in the module performing a function of determining whetherthe NDI value has been toggled. The HARQ entity 1223 may determinewhether the NDI value has been toggled, or each HARQ process 1221 maydetermine whether the NDI value has been toggled.

Through the aforementioned configuration, the problem where the userequipment determines retransmission in error after the random accessprocedure due to the NDI value received during the random accessprocedure as described with reference to FIG. 10 and FIG. 11 can besolved.

The aforementioned signal transmission and reception and theconfiguration of the user equipment for the same according to thepresent invention have been described based on the 3GPP LTE system.However, the signal transmission and reception and the configuration ofthe user equipment for the same may be applied to various mobilecommunication systems similar to the 3GPP LTE system.

It will be apparent to those skilled in the art that the presentinvention can be embodied in other specific forms without departing fromthe spirit and essential characteristics of the invention. Thus, theabove embodiments are to be considered in all respects as illustrativeand not restrictive. The scope of the invention should be determined byreasonable interpretation of the appended claims and all change whichcomes within the equivalent scope of the invention are included in thescope of the invention.

1. A method for a user equipment (UE) to transmit an uplink signal, themethod comprising: receiving a first downlink control channel identifiedby a temporary cell identifier (Temporary C-RNTI) from a base station,the first downlink control channel comprising a first uplink grantsignal having a new data indicator (NDI) with a first value; receiving asecond downlink control channel identified by a cell identifier (C-RNTI)from the base station, the second downlink control channel comprising asecond uplink grant signal having the NDI with a second value;determining if the NDI with the second value has been toggled comparedto the NDI previously received from the base station, wherein the UEignores the NDI with the first value received through the first downlinkcontrol channel identified by the temporary cell identifier (TemporaryC-RNTI); and transmitting the uplink signal based on the determining. 2.The method of claim 1, wherein the NDI previously received from the basestation comprise the NDI received through a third downlink controlchannel identified by the cell identifier (C-RNTI), the third downlinkcontrol channel received before receiving the second downlink controlchannel.
 3. The method of claim 1, wherein the second value of the NDIis associated with a specific HARQ process, and wherein the determiningcomprises determining if the second value of the NDI has been toggledcompared to the value of the NDI in a previous transmission of thespecific HARQ process.
 4. The method of claim 3, wherein transmittingthe uplink signal comprises transmitting new data by the specific HARQprocess, when the second value of the NDI has been toggled compared tothe value in the previous transmission of the specific HARQ process. 5.The method of claim 3, wherein transmitting the uplink signal comprisestransmitting retransmission data by the specific HARQ process, when thesecond value of the NDI has not been toggled compared to the value inthe previous transmission of the specific HARQ process.
 6. The method ofclaim 1, wherein the first uplink grant signal is received during arandom access procedure, and wherein the second uplink grant signal isreceived after the random access procedure.
 7. The method of claim 6,wherein the first uplink grant signal is received at a timing associatedto a first HARQ process, the random access procedure is successfullycompleted by a random access using a second HARQ process, and the seconduplink grant signal is received at a timing associated to the first HARQprocess, and wherein when determining if the NDI has been toggledcompared to the value in the previous transmission of the first HARQprocess, the UE ignores the NDI received at the timing associated to thefirst HARQ process during the random access procedure.
 8. A userequipment comprising: a physical layer module including a receivingmodule and a transmitting module, the receiving module for receiving adownlink control channel and a downlink shared channel, the downlinkcontrol channel including a new data indicator (NDI) toggled if a basestation indicates new transmission; and a MAC layer module including aplurality of HARQ process modules, a plurality of buffers respectivelycorresponding to the plurality of HARQ process modules, and a singleHARQ entity, the HARQ entity controlling the plurality of HARQ processmodules to allow a specific one of the HARQ process modules to processthe downlink control channel and the downlink shared channel received bythe receiving module and an uplink shared channel transmitted from thetransmitting module, wherein the HARQ entity or the specific HARQprocess module compares an NDI bit value previously stored in a specificbuffer corresponding to the specific HARQ process module with an NDIvalue received in correspondence with the specific HARQ process moduleto determine whether to perform retransmission depending on whether theNDI bit value has been toggled, and ignores the NDI received using atemporary cell identifier stored in the specific buffer when the HARQentity or the specific HARQ process module determines whether the NDIbit value has been toggled.